The morphogenic responses and phytochelatin complexes induced by arsenic in Pteris vittata change in the presence or absence of cadmium.

Pteris vittata L. (Chinese brake fern) is the first fern to be identified as an arsenic (As) hyperaccumulator. The fern can accumulate more than 27 000 mg As kg−1 dry weight in its fronds and for this reason it has been proposed to remove arsenic from contaminated soil and water. Lately, the capabilities of the fern to adsorb other metals such as Cadmium (Cd), in presence or not of As, has been investigated with positive results. However the morphogenic response of the fern, when exposed simultaneously to As and Cd requires insights. Both Cd and As are a potential threat for human health and the environment due to their accumulation in the soil, in the food chain and locally drinking water. Frequently, As and Cd are simultaneously present in multicontaminated environments. Arsenic is mainly present in soils in its inorganic forms, arsenate (AsV) and arsenite (AsIII) depending on the soil redox status. The plants uptake easily arsenic as AsV, and, in plant cells As V is rapidly reduced to AsIII. Cadmium is a heavy metal with no demonstrated biological function; however it enters plant roots readily. Cadmium’s chemical similarity with essential ions, such as Zn, Ca, could alter the cell’s homeostasis or displacement from proteins of these elements. As and Cd, in plant cells, cause oxidative stress, reduce glutathione (GSH) level, through the formation of As-GSH or Cd-GSH complexes and induce phytochelatin (PC) synthesis. The latter are small peptides, with synthesis induced by toxic metals, able to form complexes with metals and semimetals (as Cd and As) in order to reduce their toxicity in the cytosol. Pteris vittata is known to produce phytochelatins after As exposure. But, today, there is no information regarding how PC synthesis and PC-metal complexes formation change in the presence of As alone or combined with Cd. The aim of this research was to analyse the morphogenic responses and phytochelatin complexes induced by As in Pteris vittata in the presence or absence of Cd. The plant response has been evaluated by analyzing the As and Cd accumulation in roots and fronds, by measuring the plant biomass increase, by analyzing histologically the fronds. Futhermore the exudates extruded from the fronds were chemically analyzed to assess the contribution of the extrusion mechanism to the metals detoxification in the fern. Moreover the formation of PC-As complexes was evaluated in the fern exposed to As alone or in combination with Cd. The results show that plant morphology is strongly affected by Cd presence. In addition the simultaneous exposure to As and Cd increases the semimetal uptake while reduces the metal one in comparison with As or Cd alone. The fern extruded As and Cd from fronds but only after exposure to both elements. Besides As alone induced the same As-PC complexes in roots and fronds, when As was associated with Cd different As-PC complexes were identified in roots and fronds. In conclusion, in Pteris vittata As induces different morphogenic responses and phytochelatin complexes when associated or not to Cd.